Tablet vs. e-reader, or tablet and e-reader in one?

A friend of mine and myself have been talking about the issue of e-readers vs. tablets for some time, and I'm wondering if anyone here knows enough about e-ink technology to answer a question for me.

E-ink technology has some obvious benefits for e-readers, especially regarding power usage, contrast and readability, while being generally limited to monochrome and being somewhat slow. At the same time, LCD or LED displays have the benefits of fluidity, backlighting and colour, while having the issues of eye fatigue and excessive power usage (I know some people disagree, I won't debate it here).

Given that both have benefits and drawbacks, it would seem like having both would be ideal, should you be marketing an e-reader and a tablet in one (such as the Kindle Fire or the NOOK Tablet). So my question is this, is there anything inherent in e-ink technology that would preclude layering a transparent e-ink display over top of a capacitive LCD/LED tablet display? It would seem like this would be the best of both worlds, but I suspect that the technology is insufficient to allow this sort of fusion at this point.

I have both a Kindle reader and an iPad with the Kindle app installed. The Kindle reader is by far my preferred reader. The two biggest advantages are battery life and weight. At 8.7 ounces (247 g.), the Kindle is extremely light in weight. The iPad weighs 1.35 pounds (613 g.), which is noticably heavier.

I have a kobo ereader and use my netbook to read books as well. And I would definitely say that the e-ink screens are much easier on eye strain that conventional LCD's. And as you have mentioned they have great battery life as well. The only advantage of LCD technology is that you don't need a clip on light to read while your significant other sleeps :-/